Kidney cancer is more common in men than women and is the ninth most common cancer in men (214 000 cases) and the 14th most common in women (124 000 cases) worldwide in 2012. 70% of the new cases occurred in countries with high and very high levels of human development, with 34% of the estimated new cases in Europe and 19% in North America. There were an estimated 143 000 deaths from kidney cancer in 2012 (91 000 in men, 52 000 in women); kidney cancer is the 16th most common cause of death from cancer worldwide.
The highest incidence rates are found in the Czech Republic. Elevated rates are also found in northern and Eastern Europe, North America, and Australia. Low rates are estimated in much of Africa and East Asia. The case fatality rate is lower in highly developed countries (overall mortality-to-incidence ratio, 0.4) than in countries with low or medium levels of human development (0.5). Only 3.1% of the cases were diagnosed in Africa, but 5.7% of the deaths occurred in this region. Incidence and mortality rates have been increasing in many countries, across different levels of human development (World Cancer Report, 2014).
Most renal cancers are renal cell carcinomas (RCC), a heterogeneous class of tumors arising from different cell types within the renal parenchyma. Most are clear cell renal carcinomas (about 70% of renal cancer cases), followed by papillary (10-15%), chromophobe (about 5%), and collecting duct (<1%) renal cell carcinomas. Each of these renal cell tumor subtypes has distinct genetic characteristics (Moch, 2013; World Health Organization Classification of Tumours, 2004).
Renal cell carcinoma (RCC) is characterized by a lack of early warning signs, diverse clinical manifestations, and resistance to radiation and chemotherapy. A total of 25-30% patients with RCC initially present with overt metastases (Hofmann et al., 2005). About one third of patients with RCC will develop metastatic disease over time. Thus, nearly 50-60% of all patients with RCC will eventually present with metastatic disease (Bleumer et al., 2003; Hofmann et al., 2005). Among those with metastatic disease, approximately 75% have lung metastases, 36% lymph node and/or soft tissue involvement, 20% bone involvement, and 18% liver involvement (Sachdeva et al., 2010).
RCC patients with metastatic disease receiving cytokine-based first-line systemic therapy can be categorized into risk groups predictive for survival based on 5 prognostic factors (Motzer et al., 2004). Pre-treatment features associated with a shorter survival were low Karnofsky Performance Status (<80%), high serum lactate dehydrogenase (>1.5 ULN), low hemoglobin (<LLN), high corrected serum calcium (>10 mg/dL), and time from diagnosis to treatment <1 year. Based on these risk factors, patients were categorized into three risk groups. The median time to death in the 18% of patients with zero risk factors (favorable-risk) was 30 months. 62% of the patients had one or two risk factors (intermediate risk), and the median survival time in this group was 14 months. Patients with 3 or more risk factors (poor risk) who comprised 20% of the patients, had a median survival time of 5 months. The application of this MSKCC risk group categorization has been widely applied in clinical trials for advanced RCC. Risk categorization can be used for planning and interpreting the results of clinical trials and directing therapy.
Risk factors for RCC are cigarette smoking and obesity. Different meta-analyses confirmed that ever-smoking increases the risk of renal cancer compared with never-smoking (Cho et al., 2011; Hunt et al., 2005). There is also a dose-dependent increase in risk related to the number of cigarettes smoked per day. Risk decreases in the 5-year period after smoking cessation. Overweight, especially obesity, is a risk factor for renal cancer in both women and men (Ljungberg et al., 2011). The proportion of all cases of renal cancer attributable to overweight and obesity has been estimated to be about 40% in the USA and up to 40% in European countries (Renehan et al., 2008; Renehan et al., 2010). The mechanisms by which obesity influences renal carcinogenesis are unclear. Sex steroid hormones may affect renal cell proliferation by direct endocrine receptor-mediated effects. Obesity with the combined endocrine disorders, such as decreased levels of sex hormonebinding globulin and progesterone, insulin resistance, and increased levels of growth factors such as insulin-like growth factor 1 (IGF-1), may contribute to renal carcinogenesis. Recently, a case-control study has reported a stronger association of clear cell carcinoma with obesity (World Cancer Report, 2014).
Initial treatment is most commonly either partial or complete removal of the affected kidney(s) and remains the mainstay of curative treatment (Rini et al., 2008). For first-line treatment of patients with poor prognostic score a guidance elaborated by several cancer organizations and societies recommend the receptor tyrosine kinase inhibitors (TKIs) sunitinib (Sutent®) and pazopanib (Votrient®), the monoclonal antibody bevacizumab (Avastin®) combined with interferon-α (IFN-α) and the mTOR inhibitor temsirolimus (Torisel®). Based on guidelines elaborated by the US NCCN as well as the European EAU and ESMO, the TKIs sorafenib, pazopanib or recently axitinib are recommended as second-line therapy in RCC patients who have failed prior therapy with cytokines (IFN-α, IL-2). The NCCN guidelines advise also sunitinib in this setting (high-level evidence according to NCCN Category I).
Everolimus and axitinib are recommended as second-line therapy of those patients who have not benefited from a VEGF-targeted therapy with TKIs according to the established guidelines.
The known immunogenity of RCC has represented the basis supporting the use of immunotherapy and cancer vaccines in advanced RCC.
The interesting correlation between lymphocytes PD-1 expression and RCC advanced stage, grade and prognosis, as well as the selective PD-L1 expression by RCC tumor cells and its potential association with worse clinical outcomes, have led to the development of new anti PD-1/PD-L1 agents, alone or in combination with anti-angiogenic drugs or other immunotherapeutic approaches, for the treatment of RCC (Massari et al., 2015).
In advanced RCC, a phase III cancer vaccine trial called TRIST study evaluates whether TroVax (a vaccine using a tumor-associated antigen, 5T4, with a pox virus vector), added to first-line standard of care therapy, prolongs survival of patients with locally advanced or mRCC. Median survival had not been reached in either group with 399 patients (54%) remaining on study however analysis of the data confirms prior clinical results, demonstrating that TroVax is both immunologically active and that there is a correlation between the strength of the 5T4-specific antibody response and improved survival. Further there are several studies searching for Peptide vaccines usind Epitopes being overexpressed in RCC.
Variuos approaches of tumor vaccines have been under investigation. Studies using whole-tumor approaches, including tumor cell lysates, fusions of dendritic cells with tumor cells, or whole-tumor RNA were done in RCC patients, and remissions of tumor lesions were reported in some of thesetrials (Avigan et al., 2004; Holtl et al., 2002; Marten et al., 2002; Su et al., 2003; Wittig et al., 2001).
In the last years, several human TAAs expressed in RCCs and recognized by antigen-specific CTLs have been defined and characterized using expression cloning, reverse immunology approach, or by applying DNA microarray technology (Dannenmann et al., 2013; Michael and Pandha, 2003; Minami et al., 2014; Renkvist et al., 2001; Wierecky et al., 2006).
Considering the severe side-effects and expense associated with treating cancer, there is a need to identify factors that can be used in the treatment of cancer in general and RCC in particular. There is also a need to identify factors representing biomarkers for cancer in general and RCC in particular, leading to better diagnosis of cancer, assessment of prognosis, and prediction of treatment success.
Immunotherapy of cancer represents an option of specific targeting of cancer cells while minimizing side effects. Cancer immunotherapy makes use of the existence of tumor associated antigens.
The current classification of tumor associated antigens (TAAs) comprises the following major groups:
a) Cancer-testis antigens: The first TAAs ever identified that can be recognized by T cells belong to this class, which was originally called cancer-testis (CT) antigens because of the expression of its members in histologically different human tumors and, among normal tissues, only in spermatocytes/spermatogonia of testis and, occasionally, in placenta. Since the cells of testis do not express class I and II HLA molecules, these antigens cannot be recognized by T cells in normal tissues and can therefore be considered as immunologically tumor-specific. Well-known examples for CT antigens are the MAGE family members and NY-ESO-1.
b) Differentiation antigens: These TAAs are shared between tumors and the normal tissue from which the tumor arose. Most of the known differentiation antigens are found in melanomas and normal melanocytes. Many of these melanocyte lineage-related proteins are involved in biosynthesis of melanin and are therefore not tumor specific but nevertheless are widely used for cancer immunotherapy. Examples include, but are not limited to, tyrosinase and Melan-A/MART-1 for melanoma or PSA for prostate cancer.
c) Over-expressed TAAs: Genes encoding widely expressed TAAs have been detected in histologically different types of tumors as well as in many normal tissues, generally with lower expression levels. It is possible that many of the epitopes processed and potentially presented by normal tissues are below the threshold level for T-cell recognition, while their over-expression in tumor cells can trigger an anticancer response by breaking previously established tolerance. Prominent examples for this class of TAAs are Her-2/neu, survivin, telomerase, or WT1.
d) Tumor-specific antigens: These unique TAAs arise from mutations of normal genes (such as β-catenin, CDK4, etc.). Some of these molecular changes are associated with neoplastic transformation and/or progression. Tumor-specific antigens are generally able to induce strong immune responses without bearing the risk for autoimmune reactions against normal tissues. On the other hand, these TAAs are in most cases only relevant to the exact tumor on which they were identified and are usually not shared between many individual tumors. Tumor-specificity (or -association) of a peptide may also arise if the peptide originates from a tumor-(-associated) exon in case of proteins with tumor-specific (-associated) isoforms.
e) TAAs arising from abnormal post-translational modifications: Such TAAs may arise from proteins which are neither specific nor overexpressed in tumors but nevertheless become tumor associated by posttranslational processes primarily active in tumors. Examples for this class arise from altered glycosylation patterns leading to novel epitopes in tumors as for MUC1 or events like protein splicing during degradation which may or may not be tumor specific.
f) Oncoviral proteins: These TAAs are viral proteins that may play a critical role in the oncogenic process and, because they are foreign (not of human origin), they can evoke a T-cell response. Examples of such proteins are the human papilloma type 16 virus proteins, E6 and E7, which are expressed in cervical carcinoma.
T-cell based immunotherapy targets peptide epitopes derived from tumor-associated or tumor-specific proteins, which are presented by molecules of the major histocompatibility complex (MHC). The antigens that are recognized by the tumor specific T lymphocytes, that is, the epitopes thereof, can be molecules derived from all protein classes, such as enzymes, receptors, transcription factors, etc. which are expressed and, as compared to unaltered cells of the same origin, usually up-regulated in cells of the respective tumor.
There are two classes of MHC-molecules, MHC class I and MHC class II. MHC class I molecules are composed of an alpha heavy chain and beta-2-microglobulin, MHC class II molecules of an alpha and a beta chain. Their three-dimensional conformation results in a binding groove, which is used for non-covalent interaction with peptides.
MHC class I molecules can be found on most nucleated cells. They present peptides that result from proteolytic cleavage of predominantly endogenous proteins, defective ribosomal products (DRIPs) and larger peptides. However, peptides derived from endosomal compartments or exogenous sources are also frequently found on MHC class I molecules. This non-classical way of class I presentation is referred to as cross-presentation in the literature (Brossart and Bevan, 1997; Rock et al., 1990). MHC class II molecules can be found predominantly on professional antigen presenting cells (APCs), and primarily present peptides of exogenous or transmembrane proteins that are taken up by APCs e.g. during endocytosis, and are subsequently processed.
Complexes of peptide and MHC class I are recognized by CD8-positive T cells bearing the appropriate T-cell receptor (TCR), whereas complexes of peptide and MHC class II molecules are recognized by CD4-positive-helper-T cells bearing the appropriate TCR. It is well known that the TCR, the peptide and the MHC are thereby present in a stoichiometric amount of 1:1:1.
CD4-positive helper T cells play an important role in inducing and sustaining effective responses by CD8-positive cytotoxic T cells. The identification of CD4-positive T-cell epitopes derived from tumor associated antigens (TAA) is of great importance for the development of pharmaceutical products for triggering anti-tumor immune responses (Gnjatic et al., 2003). At the tumor site, T helper cells, support a cytotoxic T cell- (CTL-) friendly cytokine milieu (Mortara et al., 2006) and attract effector cells, e.g. CTLs, natural killer (NK) cells, macrophages, and granulocytes (Hwang et al., 2007).
In the absence of inflammation, expression of MHC class II molecules is mainly restricted to cells of the immune system, especially professional antigen-presenting cells (APC), e.g., monocytes, monocyte-derived cells, macrophages, dendritic cells. In cancer patients, cells of the tumor have been found to express MHC class II molecules (Dengjel et al., 2006).
Elongated (longer) peptides of the invention can act as MHC class II active epitopes. T-helper cells, activated by MHC class II epitopes, play an important role in orchestrating the effector function of CTLs in anti-tumor immunity. T-helper cell epitopes that trigger a T-helper cell response of the TH1 type support effector functions of CD8-positive killer T cells, which include cytotoxic functions directed against tumor cells displaying tumor-associated peptide/MHC complexes on their cell surfaces. In this way tumor-associated T-helper cell peptide epitopes, alone or in combination with other tumor-associated peptides, can serve as active pharmaceutical ingredients of vaccine compositions that stimulate anti-tumor immune responses.
It was shown in mammalian animal models, e.g., mice, that even in the absence of CD8-positive T lymphocytes, CD4-positive T cells are sufficient for inhibiting manifestation of tumors via inhibition of angiogenesis by secretion of interferon-gamma (IFNγ) (Beatty and Paterson, 2001; Mumberg et al., 1999). There is evidence for CD4 T cells as direct anti-tumor effectors (Braumuller et al., 2013; Tran et al., 2014a).
Since the constitutive expression of HLA class II molecules is usually limited to immune cells, the possibility of isolating class II peptides directly from primary tumors was previously not considered possible. However, Dengjel et al. were successful in identifying a number of MHC Class II epitopes directly from tumors (WO 2007/028574, EP 1 760 088 B1).
Since both types of response, CD8 and CD4 dependent, contribute jointly and synergistically to the anti-tumor effect, the identification and characterization of tumor-associated antigens recognized by either CD8+ T cells (ligand: MHC class I molecule+peptide epitope) or by CD4-positive T-helper cells (ligand: MHC class II molecule+peptide epitope) is important in the development of tumor vaccines.
For an MHC class I peptide to trigger (elicit) a cellular immune response, it also must bind to an MHC-molecule. This process is dependent on the allele of the MHC-molecule and specific polymorphisms of the amino acid sequence of the peptide. MHC-class-1-binding peptides are usually 8-12 amino acid residues in length and usually contain two conserved residues (“anchors”) in their sequence that interact with the corresponding binding groove of the MHC-molecule. In this way each MHC allele has a “binding motif” determining which peptides can bind specifically to the binding groove.
In the MHC class I dependent immune reaction, peptides not only have to be able to bind to certain MHC class I molecules expressed by tumor cells, they subsequently also have to be recognized by T cells bearing specific T cell receptors (TCR).
For proteins to be recognized by T-lymphocytes as tumor-specific or -associated antigens, and to be used in a therapy, particular prerequisites must be fulfilled. The antigen should be expressed mainly by tumor cells and not, or in comparably small amounts, by normal healthy tissues. In a preferred embodiment, the peptide should be over-presented by tumor cells as compared to normal healthy tissues. It is furthermore desirable that the respective antigen is not only present in a type of tumor, but also in high concentrations (i.e. copy numbers of the respective peptide per cell). Tumor-specific and tumor-associated antigens are often derived from proteins directly involved in transformation of a normal cell to a tumor cell due to their function, e.g. in cell cycle control or suppression of apoptosis. Additionally, downstream targets of the proteins directly causative for a transformation may be up-regulated and thus may be indirectly tumor-associated. Such indirect tumor-associated antigens may also be targets of a vaccination approach (Singh-Jasuja et al., 2004). It is essential that epitopes are present in the amino acid sequence of the antigen, in order to ensure that such a peptide (“immunogenic peptide”), being derived from a tumor associated antigen, leads to an in vitro or in vivo T-cell-response.
Basically, any peptide able to bind an MHC molecule may function as a T-cell epitope. A prerequisite for the induction of an in vitro or in vivo T-cell-response is the presence of a T cell having a corresponding TCR and the absence of immunological tolerance for this particular epitope.
Therefore, TAAs are a starting point for the development of a T cell based therapy including but not limited to tumor vaccines. The methods for identifying and characterizing the TAAs are usually based on the use of T-cells that can be isolated from patients or healthy subjects, or they are based on the generation of differential transcription profiles or differential peptide expression patterns between tumors and normal tissues. However, the identification of genes over-expressed in tumor tissues or human tumor cell lines, or selectively expressed in such tissues or cell lines, does not provide precise information as to the use of the antigens being transcribed from these genes in an immune therapy. This is because only an individual subpopulation of epitopes of these antigens are suitable for such an application since a T cell with a corresponding TCR has to be present and the immunological tolerance for this particular epitope needs to be absent or minimal. In a very preferred embodiment of the invention it is therefore important to select only those over- or selectively presented peptides against which a functional and/or a proliferating T cell can be found. Such a functional T cell is defined as a T cell, which upon stimulation with a specific antigen can be clonally expanded and is able to execute effector functions (“effector T cell”).
In case of targeting peptide-MHC by specific TCRs (e.g. soluble TCRs) and antibodies or other binding molecules (scaffolds) according to the invention, the immunogenicity of the underlying peptides is secondary. In these cases, the presentation is the determining factor.